This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Transcription is the first step and the key control point in the pathway of gene expression. Transcriptional regulation underlies development, oncogenesis, and other fundamental processes. In eukaryotes the enzyme RNA Polymerase II (pol) is responsible for transcription of messenger RNA making pol?s regulation central to gene expression. During the period of this proposal we will continue our structural studies of the pol transcription machinery. These studies are currently proceeding along three avenues: first, detailed analysis of the elongating pol II using mutation analysis;second, co-crystals of pol II with initiation and elongation factors;third, structural studies of the mediator complex, a 22 polypeptide complex required for pol to respond to regulating proteins.